Sodium chloride and alkali metal salts such as calcium chloride are used extensively and in large quantities on roads for melting snow and ice. These agents work well in deicing applications, but have several drawbacks. For example, salt is a leading cause of structural corrosion of the nation's bridges and highway structures and spalling of concrete. Salt also causes severe vehicle corrosion and is also harsh on the environment. Thus, it would be highly desirable to develop an alternative deicer composition that is readily biodegradable at relatively cold temperatures, has considerably less residual impact on structural corrosion of the nation's highways and bridges, causes less spalling of concrete, and is less harsh to the environment.
Calcium magnesium acetate (hereafter CMA) has been tried as one alternative deicer. Unfortunately, CMA spontaneously generates free acetic acid, even at pH values as high as 9, via the hydrolysis of the acetates group by an alkaline reaction. CMA is also very dusty; thus, personnel handling CMA should wear appropriate masks. Also, the exposure of personnel to acetic acid fumes is quite undesirable. Another problem with CMA is that it draws frost due to its hygroscopic nature; thus, areas that normally would tend to dry out during daylight hours remain wet and may refreeze during colder nighttime temperatures. Therefore, CMA is not a preferred or generally acceptable alternative to sodium chloride as a deicing composition. Sodium acetate, another potential deicer, also undergoes hydrolysis to release free acetic acid.
Another composition which has been used as a deicer composition is disclosed in Sandvig et al., U.S. Pat. No. 4,664,832. This patent discloses a deicer composition manufactured by reacting sodium carbonate with sawdust or other lignocellulose biomass at elevated temperatures. The manufacture of the composition of this patent generally requires high temperatures and pressures and the evaporation of large volumes of water. The resulting mixture, which contains sodium salts of acetic, formic, glycolic, and lactic acids, has an acceptable freezing point depression, but has limited ice penetration capability. Ice penetration using this composition ranges from between about 0 to about 66 percent of the values obtained with sodium chloride under similar test conditions. The Sandvig et al. composition is not, therefore, as effective a deicer as sodium chloride. Furthermore, these deicing compositions can vary considerably in both specific composition and effectiveness due to inherent compositional differences and variations in the biomass feedstock.
Palmer, Transportation Research Record 1127, 1987 (published by Amoco Chemicals Company, P.O. Box 400, Naperville, Ill. 60566) indicated that sodium formate should be investigated as a potential deicer and that it could be a better alternative to CMA. Sodium formate has a freezing-point curve similar to sodium chloride down to about -14.degree. C. Sodium formate was reported to be of particular interest because it potentially could be applied in solution form in the airline industry as a deicer for both planes and runways. But sodium formate is not as effective as sodium chloride as a deicer and is corrosive.
It would be desirable, therefore, to provide deicing compositions that are relatively inexpensive, that do not have a high corrosive potential or spalling effect, that are environmentally friendly, that are essentially non-dusty, and that have substantial freezing point depressions and good ice penetration characteristics. The compositions and methods of this invention generally provide such characteristics.